1. Field of the Invention
The present invention relates to a magnetic disk drive apparatus provided with a magnetic disk and a magnetic head for writing information onto the magnetic disk, to a mobile phone or a vehicle-mounted system with the magnetic disk drive apparatus, and to a method for compensating characteristics of the magnetic disk drive apparatus.
2. Description of the Related Art
Japanese patent publication No. 2001-093104A discloses an error recovering method for correcting imbalance in magnetic domain of a magnetoresistive effect (MR) read head element of a magnetic head in a magnetic disk drive apparatus. The imbalance is corrected by moving the magnetic head into a contact-start-stop (CSS) region of the magnetic disk and performing dummy write of an inductive write head element.
Japanese patent publication No. 10-134305A discloses a method for stabilizing change in output wave-shape of an MR read head element of a magnetic head in a magnetic disk drive apparatus. The wave-shape is stabilized by moving the magnetic head into a dummy write region and performing dummy write of an inductive write head element with a write current that is larger than the normal write current under supplying a sense current that is larger than the normal sense current to the MR head element.
Japanese patent publication No. 2003-036502A discloses a method for recovering characteristics of an MR read head element of a magnetic head in a magnetic disk drive apparatus. In case that a write magnetic field from an inductive write head element is applied to the MR read head element to deform its output signal shape, recovering of the characteristics of the MR read head element is performed by temporally resting the magnetic head in an evacuation region of the magnetic disk and executing dummy write of the inductive write head element.
Recently, a magnetic disk drive apparatus is beginning to be assembled in a mobile equipment such as a vehicle-mounted equipment of for example a car navigation system or a car audio system, or a mobile phone. In such case, the magnetic disk drive apparatus is required to operate under harsher environments as compared with when assembled in a walkabout computer.
If the magnetic disk drive apparatus is left for a long time under a low temperature environment of 0° C. or −20° C. and/or under a high temperature environment of 80° C. or 100° C., inner stress of the magnetic head will change due to a difference between expansion coefficients of materials used. This change in the inner stress will induce magnetostriction in an upper shield layer or a yoke in the magnetic head, which is made of a magnetic material causing the magnetic characteristics of the write head element to deteriorate. Thus, normal operation of data writing just after startup of the magnetic disk or the magnetic disk drive apparatus cannot be expected causing occurrence of operation error. External magnetic stress due to some reason other than the low or high temperature may be applied to the magnetic head causing the magnetic characteristics of the write head element to deteriorate.
All of the aforementioned conventional dummy write methods intend to recover characteristics of MR read head elements by providing a dummy write current that is equal to or larger than the normal write current to inductive write head elements but do not intend to prevent magnetic characteristics of the write head elements from deterioration. If such conventional dummy write methods are performed, because no air-cooling effect due to the rotation of the magnetic disk is expected, the temperature of each magnetic head will extremely increase. Thus, when the dummy write current that is equal to or larger than the normal write current is applied to the inductive write head elements, the MR read head elements may be rather damaged.